Project Summary/Abstract Our U01 CREATE grant supported development of BIIB105, an ATXN2 antisense oligonucleotide (ASO) for treatment that is now in a phase 1 trial for amyotrophic lateral sclerosis (ALS). We are now proposing to expand the ATXN2 target space by developing ASOs to STAU1. STAU1 interacts with ATXN2, and is overabundant in multiple in vitro and in vivo models of neurodegeneration. Our proof-of-concept data showed positive PD efficacy, in that lowering STAU1 modifies disease-related phenotypes. ATXN2[Q127] SCA2 mice haploinsufficient for Stau1 had normalized cerebellar gene and autophagy protein abundances, ATXN2 protein aggregates were eliminated, and motor behavior was improved. In addition, the abnormally slow intrinsic Purkinje cell (PC) firing frequency in SCA2 mice is restored following Stau1 ASO treatment. STAU1 expands the ATXN2 target space and may prove more effective as a therapeutic target for ALS and other TDP-43 proteinopathies as its protein abundance is increased 3-4 fold in multiple in vitro and in vivo neurodegenerative models including sporadic ALS spinal cord. We have already screened for ASOs targeting STAU1, identifying 10 top leads that lower STAU1 expression by 90-99% in SCA2 patient fibroblasts, including two potent ASOs that also target mouse Stau1 invaluable for in vivo efficacy studies in disease models. Our overall objective is to optimize ASO sequence and chemistry for lowering STAU1 expression, and to refine an in vivo efficacy models for characterizing target engagement and PD/PK parameters in vivo. Currently, no therapeutics exist that significantly modify sporadic ALS. STAU1 is overabundant in multiple neurodegenerative disease models, and Stau1 knockdown by genetic interaction improves in vivo phenotypes. The R61 phase of our study will span one year and is organized in two aims: Aim 1 will prepare sequence optimized chemically-modified ASOs for efficacy testing in BAC-STAU1 mice and Prp-TDP43Q331K mice. Aim 2 refines the use of Prp-TDP43Q331K mice for characterizing efficacy of STAU1 ASO, resulting in optimal doses required for effective STAU1 knockdown and phenotype modification. The R33 phase spans the remaining two years of the study and is comprised of two additional aims: Aim 3 will demonstrate that lead ASOs modify TDP-43 abundance & solubility, normalizes autophagy markers, histological phenotypes and motor neuron counts and motor behavior of Prp-TDP43Q331K mice. Aim 4 will determine ASO effects for improving survival for three most efficacious lead ASOs using Prp- TDP43WTxQ331K double transgenic mice. The terminal milestone for this study will be validation of in vivo efficacy for three optimized ASOs with long duration of action for Staufen knockdown, and efficacy data for additional ASO sequences useful or future investigation. The crucial objective is the identification of lead STAU1 ASOs that modify an ALS neurodegenerative phenotype suitable for advancing to a URGenT or Blueprint Neu...